Help me find this episode.

Here is all I can remember. An alien race makes their ship look like a federation ship. The crew board it, discover it is not quite like it should be. The doctor is left there assisting. In the end the ship transforms back to how it was.

Well hope and fear was the episode that had the alien ship, but I am still trying to find the one where the EMH beams over and I think he might have activated another ships EMH and solved the problem together. I sure has been too long. My memory has failed me.